The present invention relates to an electric vehicle.
In recent years, from the viewpoint of low pollution, attention has been paid to electric vehicles such as electric cars or hybrid cars, which travel while driving motors with electric power from secondary batteries. For example, a so-called hybrid vehicle includes a battery having a plurality of secondary batteries connected in series with each other, a motor generator that operates with electric power from the battery and supplies electric power to the vehicle, and also functions as an electric generator during regeneration, and an engine that operates with fuel. The vehicle of this type is driven by an output from the engine or the motor generator, or a total output of the engine and the motor generator.
The motor generator and the battery are connected to each other through an inverter. The inverter converts a DC power supplied from the battery into an AC power, for example, under a PWM control, and supplies the AC power to the motor generator, and controls the drive of the motor generator.
As a related-art control device for the electric vehicle, there is, for example, a battery voltage adaptive electric vehicle control device that includes control means for controlling a motor voltage according to an instruction of a driver who drives an automobile and a travel speed of the automobile. The control device controls a motor voltage to change the highest speed set value for enabling the travel of the vehicle according to a battery voltage so that a travel speed falls within the highest speed set value, and also notifies the driver of the highest speed set value (for example, refer to Japanese Patent No. 3200885). The control device disclosed in Japanese Patent No. 3200885 can provide the electric automobile that is safe and high in reliability by notifying the driver of a change in performance of the electric automobile driven by the motor.
In the control device disclosed in Japanese Patent No. 3200885, even when the battery voltage is reduced to a given value or lower, safe driving can be conducted according to the performance by notifying the driver of a change in the performance of the automobile.
Incidentally, when the battery voltage is reduced in the electric vehicle, it is conceivable that there occurs not only the above problem but also the following problem. That is, when the vehicle travels to rotate the motor generator, an induced voltage is developed by the motor generator. However, if the vehicle speed is high when the battery voltage is low, the induced voltage developed in the motor generator may be higher than the battery voltage. In this case, in order to prevent a current generated by the induced voltage of the motor generator from flowing into the battery, the inverter controls the rotation number of the motor generator to limit the induced voltage developed in the motor generator so that the induced voltage becomes lower than the battery voltage.
However, when a trouble (for example, failure in a diode) occurs in the inverter, the induced voltage thus developed in the motor generator cannot be limited, and the current generated by the induced voltage of the motor generator is allowed to flow into the battery, as a result of which a regenerative torque is generated. This suffers from such a problem that there is a possibility that unintentional deceleration occurs during high-speed travel to extremely deteriorate the stability of the driving.